Selecting a ControlLogix controller

In this section, we will detail the Logix software versions that are compatible with the various ControlLogix series and the currently active series.

When selecting a ControlLogix controller, it is important to consider the following:

• The supported Logix Designer software versions
• The processing requirements of your current application and future expansion
• The memory requirements of your current application and future expansion

ControlLogix Series 6, 7, and 8 controllers and their software version compatibilities are detailed as follows:

Rockwell classifies their products' life cycle statuses using the following terminology:

• Active:Most current/latest offering within a product category.
• Active Mature:A product that is still fully supported, but a newer product or family exists that can directly replace it.
• End of Life: A product discontinued date has been announced and the customer should consider migrations and last-time buys. The product can still be purchased until the official discontinued date, although inventory outages on specific items may occur.
• Discontinued: The product is no longer manufactured and it is unlikely that you can purchase the product (and if you can, it will be very expensive). Support, repair, or exchange services may still be available.

As you can see, the Series 6 (L6) controller has been discontinued. However, I will continue to reference this model as I still personally use this model in my own lab. Furthermore, it is relatively easy to find these controllers on eBay for your own testing and development projects.

Now that we have covered the various Logix controller hardware at a high level, let's take a look at the supporting software and firmware versions in the following section.

ControlLogix software and firmware

Due to the long lifespan of most industrial PACs, it is common to encounter controllers that still run legacy firmware. Controller firmware versions and RSLogix 5000 and Logix Designer versions go hand in hand. If you are working on ControlLogix or a CompactLogix controller that is running firmware version 13.03, you should use RSLogix 5000 version 13.03 to program it. As updating firmware can introduce process downtime, it is important to understand and work with the capabilities of older firmware and software versions of RSLogix 5000 and Logix Designer.

The following table details some of the major changes with each firmware release over the past two decades of ControlLogix:

Now that we have covered a brief overview of the changes introduced in each Logix firmware version, in the next section, we will detail the meaning of the lights, key switches, and LED displays on the controller CPUs.

Key switches, lights, and character displays

All of the ControlLogix family controllers have status lights and keys, and the L7 and L8 series even have four character displays. Let's now take a look at what the various status codes and messages mean and what information they provide to operators.

The following diagram shows the L5 controller status lights and key positions:

In the next section, we will detail the meaning of each of the three key position values illustrated in the previous diagram (RUN, REM, and PROG).

Key switches

Key switches control the operating mode of a PLC. A key is used to change the operating mode because changing the mode can potentially interrupt a running process.

All ControlLogix controllers have a key switch with the following three positions:

• RUN:While the key switch is in RUN mode, logic is executing, inputs are being read, logic is being scanned, and outputs are actively being controlled. Values in the program can be changed through the data monitor or by using the I/O force table. The program and operating mode and program logic cannot be changed remotely while the key switch is in RUN mode.
• REM (remote): Selecting REM mode allows the processor run mode and logic to be changed remotely using an Ethernet or serial connection while the PLC is online. The controller still continues to run as it would normally in RUN mode.
• PROG (program): When the key switch is in PROG mode, the program logic stops executing, outputs are not controlled, and the program can be edited remotely using a serial or Ethernet connection. The health LED will flash green on any output module in your rack when the CPU is in PROG mode.

Internally, within the Studio 5000 software, there is also a test mode, where inputs are read, logic is scanned, and outputs are controlled but are ignored by the actual I/O modules.

Turning the key from RUN or REM to PROG will cause the PLC to stop the running process. This could have disastrous consequences depending on the nature of the process being controlled. It is best to avoid turning the key while working on a running process just in case you accidentally bump it to PROG mode. Furthermore, it is also possible, when you switch to PROG mode, that the output that is currently active will remain on.

Lights

There are several different status lights that appear on ControlLogix controllers:

• RUN:When the RUN status light is off, the controller is in program or test mode. When the RUN status light is steady green, the controller is in RUN mode.
• I/O:When the I/O light is off, this means that either there are no I/O devices configured in the controller's program or no program has been loaded into the controller. When the I/O light is solid green, the controller is communicating with its configured I/O devices. When the I/O light flashes green, this indicates that one or more of the configured I/O devices are not responding. A flashing red I/O light indicates that a chassis fault exists and it may need to be replaced.
• RS232: The RS232 indicator shows whether the serial port is in use. The indicator light will be off if there is no serial activity but will flash green when a serial connection is active.
• BAT:The BAT indicator shows the charge of the battery and the status of the program that is saving to non-volatile memory. The BAT indicator will shine green when the program is being stored in non-volatile memory during power down. The BAT indicator will glow red when the battery is not installed or is 95% discharged.
• FORCE: The FORCE indicator shows whether I/O forces are active or enabled within the controller. A forced value is a value within the program that is being overwritten and disregarding any changes made to it by the program logic. When the indicator glows a steady amber, this means that I/O forces are active and enabled. A flashing amber light indicates that a force is active but not enabled.
• OK: The OK indicator shows the state of the controller and, when it is glowing solid green, this means that the controller is in a normal state. When the OK indicator is flashing red, the controller either requires a firmware upgrade or a major fault has occurred that has stopped the logic from executing. When the OK indicator is solid red, this usually means that the controller is powering up, is unable to power up, or a program is being loaded in memory.
• SD: The SD indicator light shows whether the SD card is in use.
• NET: The NET and LINK indicators show the state of the Ethernet/IP port on the L8 controller. When the NET light is off, the controller does not have an IP address, or the link has been disabled. When the indicator is flashing green, the controller has an IP address, but no connections have been established. When the indicator light is steady green, the controller has an IP address and at least one active connection. A steady red color means that a duplicate IP address exists or that there is an invalid network configuration.
• LINK: When the LINK light is off, this means there is no physical Ethernet/IP connection to the controller or the port has been disabled. A flashing green light indicates network activity on the port.

Character displays

The four-character display that appears on the L7 and L8 series controllers can provide a plethora of information about the controller.

The following is a diagram of the four-character display on the L7 controller:

The following is a diagram of the four-character display on the L8 display:

The following modes display on the four-ASCII-character display found on the L7 and L8 controllers:

• TEST: The controller is in TEST mode.
• PASS: Power-up testing has completed successfully.
• SAVE: A ControlLogix project is being saved to the SD card.
• LOAD: A ControlLogix project is being loaded from the SD card.
• UPDT: A firmware upgrade is being performed.
• CHRG: The capacitor-based ESM module is being charged.
• REV: Displays the major and minor versions of the firmware running on the controller.
• No Project: No ControlLogix project is currently loaded on the controller.
• Project Name: The name of the currently loaded ControlLogix project.
• BUSY: The I/O modules are not fully online yet.
• Fault Code Information: Major faults and I/O module faults will also be displayed on the four-character LCD panel.

Now that we have a solid understanding of the features, capabilities, and display functions of ControlLogix controllers, we will introduce an online tool to help you select compatible components and download firmware. This tool is called the Rockwell Automation Compatibility and Download Center and we will explore it in the following section.